1. Field of the Invention
The invention relates to a method for transmitting data using an Ethernet AVB transport protocol between nodes of a motor vehicle that, in particular, may at least to some extent also be in the form of controllers of the motor vehicle. The transmission of data by the Ethernet AVB transport protocol has provision for data to be transmitted at cyclic intervals via an Ethernet-based network by inputting the data into a transmission frame, also called an MAC frame, and forwarding them to local transmitters of a node of the motor vehicle. The AVB transport protocol has provision for, prior to the data being sent, the resources that are necessary for the transmission of the data, particularly the data rate and the transmission rate, to be reserved by reservation messages from a dedicated (separate) protocol, particularly what is known as the MSRP (Multiple Stream Reservation Protocol), wherein the flow of data from a node, particularly in the case of reservation by what is known as traffic shaping, is set to a particular transmission rate and/or data rate.
The method has provision for the local transmitters and receivers of a node, which are also called PHY devices and particularly accomplish the bit-by-bit data transmission in the physical layer, to be deactivated in non-use periods, in which no data need to be transmitted, and activated again provided that data are pending transmission in a transmission frame (MAC frame) from an upstream layer, particularly what is known as the MAC layer, wherein the local transmitters and receivers (PHY devices) are available for transmission following an activation time.
2. Related Art
Besides the typical bus systems in the automotive field, such as CAN bus, FlexRay or the like, the bus system operating on the basis of an Ethernet transport protocol is also increasingly finding its way into the motor vehicle. The Ethernet, i.e., a network that operates on the basis of the Ethernet transport protocol, and is usually wired, has a high data rate, is highly flexible and has worldwide standardization. Therefore, the Ethernet will also be an important system interface for a motor vehicle in the coming years.
The increasing electrification of motor vehicles also means an increasing rise in the power requirement thereof. This in turn results in increased fuel consumption, which has a direct effect on the end user in terms of cost. In addition, taxation on a motor vehicle today is calculated on the basis of CO2 (carbon dioxide) emissions, which can in turn be derived from the energy consumption in terms of fuel. The range of an electrically operated vehicle is also coupled to the capacity of the battery and hence to the power requirement of the loads connected in the motor vehicle.
During standard network operation, the local transmitters and receivers (PHY devices), which are also called Ethernet transceivers, have a constant power requirement that is independent of the utilization level of the connection in the data transmission, since what are known as IDLE code groups are sent when no useful data need to be transmitted via the data connection.
A new IEEE 802.3az standard (also called energy efficient Ethernet—EEE) provides expansions in order to deactivate the transmission of IDLE code groups in the local transmitters and the receivers on the other side of the communication connections during the periods without useful data transmission instead of continuing to send the IDLE code groups. This deactivation is also called Low Power Idle—LPI (energy saving mode). This allows the power requirement to be reduced in the physical layer, which produces the actual data transmission.
The aforementioned standard also stipulates the minimum transmission time between the normal state of the Ethernet transceiver, in which data transmission can take place, and the deactivated mode (LPI). In this case, the time for waking or activating a transmitter and/or receiver from the energy saving mode (LPI) is specified at 30 μs. This time is called the waking or activation time Tw. In addition, a changeover time is stipulated that is needed in order to transfer the local transmitter and/or receiver to an energy saving mode (LPI state). This deactivation time Ts is 200 μs according to the provided standard. The activation time Tw and the deactivation time Ts are the minimum values according to the standard and cannot be reduced, in order to remain compliant with the standard. Compliance with the standard is necessary in order to achieve a universal communication capability among the devices.
In order to save energy from an Ethernet AVB connection (Ethernet Audio Video Bridging), US 2011/0090914 A1 proposes a method in which an energy-efficient network (EEN—Energy Efficient Networking) is negotiated. In this case, the MAC controllers and the PHY transceivers negotiate a data rate for the connection, with a lower data rate reducing the power consumed by the transceivers. In order to maintain the connection and to avoid complex tuning of the PHY transceivers among one another (training), time windows of the Ethernet AVB connection are regularly used in order to update configuration parameters and/or training information. The disadvantage in this case, however, is that the data rate needs to be known beforehand in order to afford an appropriate setting option.
EP 2 073 464 A1 discloses a method in which the PHY transceivers transmit data on different data channels. When the data packet traffic is relinquished, some channels can be shut down or reset to an idle mode with relatively low energy consumption, the proposal being made that one or more of the quiet channels be used for transmitting control signals.
In an Ethernet network, the transceivers (Ethernet transceivers, PHY devices) in a first protocol layer (PHY layer), also called physical layer, allow the actual communication between connected network subscribers by physically sending and receiving the data packets. The connection control is performed in a second protocol layer (MAC layer, media access control layer, which is upstream of the first protocol layer), also called data link layer, by MAC controllers. The MAC controllers of the second protocol layer form transmission frames (MAC frames), in which the actual data are then compiled on a bit-by-bit basis and transmitted to the actual data transmission to the PHY layer. Data transmission takes place only when a transmission frame (MAC frame) in the second protocol layer is pending transmission. In order to maintain the data connection, IDLE packets or IDLE code groups are sent when there are no data pending transmission. The actual applications, for example in controllers, are then found in protocol layers further upstream of the second protocol layer.
The Ethernet AVB transport protocol IEEE 1722 is increasingly becoming of interest in use in motor vehicles. This protocol sends data via an Ethernet-based network at cyclic intervals. Before the actual sending of the data, the required resources, for example the data rate and/or the transmission rate from the local transmitter to the local receiver, are reserved.
In particular, this is performed for the dedicated MSRP protocol (Multiple Stream Reservation Protocol), which is part of the AVB standard 802.1Qat. This propagates the transmission cycle, inter alia. Typical transmission rates are 125 μs, which is significantly shorter than the minimum transmission cycle comprising activation time Tw and deactivation time Ts.
Traffic shaping is a further function of the Ethernet AVB standard which is implemented by the Q802.3Qav standard. Traffic shaping affords the opportunity to control the flow of data from a node of the network, with a particular transmission rate and/or data rate being set. The basic idea of traffic shaping is to delay data packets arriving too quickly from the upper protocol layers in order to initiate uniform transmission to the physical transmission devices of the physical layer. This reservation message and the parameters contained therein set and adjust the traffic shaper of the respective output ports.
Since the typical transmission rate is higher than the minimum transmission cycle comprising activation time Tw and deactivation time Ts in this mode, however, it is not possible to save any power or any energy in this mode. Instead, the data packets are merely delayed. The realtime response of the Ethernet AVB standard is thus adversely affected by the energy efficient Ethernet EEE. The underlying problem is the activation time Tw that is always needed when leaving the deactivated state of the local transmitters and/or receivers in order to activate the local transmitters and receivers. According to the proposed standard, a local transmitter and/or receiver leaves the deactivated state only when a transmission frame (MAC frame) in which data are intended to be transmitted is available. Since the upper (upstream) layers of the data transmission protocol (communication model) are largely decoupled from the physical data transmission, it is thus always possible for a delay in the activation time Tw in the order of 30 μs to arise, for example in order to activate the local transmitter. It is then necessary for a transmission frame to wait, and the transmission frame is delayed by this time.